tests: no need to reference khmer font directory for bug2037
python bindings: reduce compile times by consolidating code in fewer cpp files
use std namespace for math functions
add support for geometry-transform in pattern symbolizers - closes #2065
update changelog afer #2065
update copyright year for scons build files
upgrade clipper from 5.1.5->6.0.0
fix #1846 in 2.3.x branch for unix (msvc still a mystery)
png_reader ensure we throw early if a file_source cannot be opened
best practice: lways define NOMINMAX when including windows.h
png_reader: quote filenames in error output
travis: test all branches
Merge branch '2.3.x' of github.com:mapnik/mapnik

Conflicts:
	bindings/python/mapnik_building_symbolizer.cpp
	bindings/python/mapnik_debug_symbolizer.cpp
	bindings/python/mapnik_line_pattern_symbolizer.cpp
	bindings/python/mapnik_line_symbolizer.cpp
	bindings/python/mapnik_markers_symbolizer.cpp
	bindings/python/mapnik_point_symbolizer.cpp
	bindings/python/mapnik_polygon_symbolizer.cpp
	bindings/python/mapnik_python.cpp
	bindings/python/mapnik_raster_symbolizer.cpp
	bindings/python/mapnik_shield_symbolizer.cpp
	bindings/python/mapnik_symbolizer.cpp